In man, hemoglobin (HB) production switches from fetal (alpha2 gamma2) to adult (alpha2 beta2) during ontogeny. This switch is reversed in hematologic stress. Manipulation offers therapeutic potential in sickle cell disease and thalassemia. The mouse model proposed here may provide understanding of the switching mechanism. Some strains have major (alpha2 beta2-major) and minor (alpha2 beta2-minor) HBs. The minor/major ratio may decline during ontogeny, and change in adults with experimentally altered erythropoiesis. Friend murine erythroleukemia cells (ELCs) provide an in vitro model. In differentiated cells, the minor/major ratios are specific for inducing agent and cell line, and reflect changes in intracellular globin mRNA. The ELC system will be examined to determine whether globin regulation is due to altered transcription or processing, or to selective growth of cells preprogrammed for specific globin chains. Methods include cell cloning, and examination of HB in single cells with specific antisera, cross-linking agents, and electrophoresis. Another in vitro system involves culture of normal erythroid progenitors in semisolid media. If the mouse minor/major ration is altered (as the gamma/beta ratio is in man), the system can be used to determine whether regulation is transcriptional or clonal. Information derived from erythroid studies will then be applied to murine erythroblasts fused with heterologous fibroblasts, in an effort to activate globin production in non-erythroid cells. This would have application to the prenatal diagnosis of hemoglobinopathies. The studies in this proposal will develop murine in vivo and in vitro models for the human HB switch, and provide basic information about cellular or molecular regulation.